This invention relates to a shutter of a camera having an opening member for opening a shutter aperture and a closing member for closing the aperture, and particularly to a focal plane shutter for shielding the aperture from light by both of the opening member and the closing member immediately after termination of film exposure.
2. Description of the Prior Art
Focal plane shutters in which each of an opening member and a closing member comprises a plurality of blades have been widely used in cameras because of their compactness. In such focal plane shutters, before exposure, the opening blades of the opening member cover the aperture while being spread so as to partly overlap each other and at this time, the closing blades of the closing member are folded outside the aperture so as to completely overlap each other, and after exposure, the opening blades are folded outside the aperture and the closing blades cover the aperture while being spread. A slight quantity of light may leak from the area of partial overlap of each of the spread opening blades or closing blades and reach the film. Usually, this quantity of leakage light is negligible, but for example, where the object to be photographed includes the sun or high speed film is used, the quantity of leakage light becomes innegligible. Also, where the opening member or the closing member comprises a single blade, if plastics is used for the blade in order to make the blade light in weight, the leakage light will pose a problem because of the poor light-intercepting property of plastics.
To solve the problem of such leakage light, in the focal plane shutter disclosed in U.S. Pat. No. 4,114,174, the aperture is covered by both of the opening member and the closing member before exposure and after exposure. This shutter is provided with two springs for driving the opening member and two springs for driving the closing member, and in response to a shutter release operation, the first one of the four springs retracts the closing member from the aperture and subsequently, the second one of the four springs retracts the opening member from the aperture, thereby starting film exposure. After lapse of a predetermined exposure time, the third one of the four springs drives the closing member to cover the aperture and immediately after the exposure has been completed, the fourth one of the four springs drives the opening member to cover the aperture. However, this shutter has a disadvantage that a great force is required for shutter charge because the four springs must be charged at a time during shutter charge, and also has a disadvantage that the structure thereof is complicated because the use of the four springs necessitates the provision of a mechanism for restraining these springs in their charged state and releasing the restraint of the springs in succession.